use a program like Magic ISO to replace the file \ECS\INSTALL\REGISTER.DLL in eCS20_cd1_en_us.iso with the one from eCS 2.0 RC7.

Now you can install with the following data:
Username: EN12up20
Serial: 00000000000-00000000000-00000000000-00000000000-00000000000-00000000000-00000000000-00000000000

Beware: the input boxes take an input longer than visible. Be carefull not to enter too many zeros in the boxes.